By steps big and small, China is changing the balance of power in the world.

It is modernising its military and expanding its reach with mobile launchers that could fire missiles into the American north-west and a navy and air force that could operate well beyond its borders.

None of this has escaped the notice of the United States which is calculating how to respond to China's emergence as a strategic power.

Shifting balance of power

In the strange calculus nations use to measure strategic power, individual pieces of equipment can have radical, even world changing, implications.

China, for example, has long possessed ballistic missiles with nuclear warheads. But in the last few years China has developed a system to launch those missiles from trucks.

The system is called a Transporter-Erector-Launcher, or TEL. The missile it carries is called a Dongfeng-31. "Dongfeng" means East Wind.

The TEL not only transports the DF-31. The missile is erected and then launched from the vehicle. The entire system is mobile.

"This means in a crisis China can disperse its ballistic missile forces and have a high degree of confidence some of it would survive a pre-emptive strike by a foreign power," says James Mulvenon, who heads a new private think tank in Washington, the Center for Intelligence Research and Analysis (Cira).

US analysts believe the DF-31 will be deployed in the next few years. They also believe the missile has the range to hit the north-western United States.

"This in a broader sense gives China a true survivable nuclear deterrent and the confidence that goes along with that in terms of its military policy and the conduct of its national security policy abroad," says Mr Mulvenon.

For the United States, the advent of such a system begins the shift in the strategic equation.

Flashpoint Taiwan

And it is not only DF-31s that are reshaping the strategic landscape.

China is thought to be close to developing an effective in-flight refuelling capacity.

That will give its air force a much longer range. It is investing in submarines, and in command and control systems which it hopes will allow it to compete on a high technology battlefield.

China is determined not to allow Taiwanese independence

China's new confidence will show itself in the coming years. We will probably see the Chinese navy moving to secure sea lanes and oil supplies from the Middle East.

We will see its air force roaming much further from home, monitoring other forces in the region.

And, maybe, we will see China really gearing up to retake Taiwan by force.

The head of the CIA, Porter Goss, told Congress recently that his agency believes China is ready to fight for Taiwan.

"China's military build-up threatens the balance of power in the Taiwan Strait," said Mr Goss.

If Taiwan, in its efforts to establish a true, independent nationhood, pushed Beijing beyond the limits of its tolerance, "we assess that Beijing will respond with varying degrees of force," he said.

The last thing America needs now - with its military already extended in Iraq and Afghanistan - is to be sucked into a conflict with China over Taiwan.

When, a week ago, China announced that, for a fifth year in a row, it was increasing its military spending, there was not much surprise in Washington, but a perennial anxiety over China's long-term intentions was reinforced.

"The bottom line is what these annual increases tell us about intent," says Cira's James Mulvenon.

"[The Chinese] believe the potential for a conflict with the US over Taiwan is a very real scenario. And they have to have real, credible, concrete military options should that occur," he said.

China says publicly that it will spend about $30bn this year on its military. Analysts in the US suspect the real figure is perhaps half as much again.

Even so, China's military spending is only about one-tenth of what the US is due to spend in the coming year.

But in preparing for a "Taiwan scenario", the Chinese have a focussed objective, which allows them to channel their spending towards specific, rather than contingency, plans.

Trans-Atlantic friction

If America's strategic preoccupations with China are long-term, there exist short-term preoccupations that threaten the equilibrium of this delicate, changing relationship.

China has announced a planned "anti-secession law" aimed at preventing a formal statement of independence by Taiwan, and reinforcing the threat of force.

The EU is keen to secure Airbus deals in China, US senators say

A White house spokesman has called the planned law "unhelpful", and has asked China to "reconsider".

And the US considers equally unhelpful a plan by European countries to lift the arms embargo on China, which was imposed in 1989.

US analysts say sensitive technology could fall into Chinese hands if European countries recommence selling weapons systems to China.

They worry particularly that some European battlefield communication and command and control systems are designed to operate alongside US systems.

Purchasing those European systems, they argue, could allow China insight into the way the US military operates.

And in Congress, they smell a rat.

The Chairman of the Senate Foreign Relations Committee, Richard Lugar, told the BBC he believed the Europeans were simply trying to curry favour with Beijing in order to win lucrative business contracts for companies like Airbus.

"Folks weren't born yesterday in this country," he said. This has the makings of a major trans-Atlantic row.

But it is a measure of China's leverage and its attractiveness as a business opportunity that Europe would risk a diplomatic spat with the United States.